It is known, as disclosed in U.S. Pat. No. 4,362,214, to provide an orifice well safety valve which will close when the differential pressure caused by the flow through a reduced inside diameter choke bean reaches a predetermined level. Such valves can be adjusted to close at different flow rates by changing the spring values which serve to hold the valve open, and/or varying the internal diameter of the choke bean.
However, in some cases, the choke bean may have a large area on which the differential pressure acts, such as the case in using a wireline insertable and removable choke bean. The larger area subsequently causes a larger restraining force to be required to keep the valve open during normal flow conditions. The magnitude of the forces required cannot be conveniently generated by a coiled compression spring commonly used in orifice-type valves.
The present orifice safety valve utilizes a spring-loaded releasable latch which engages the flow tube yieldably preventing the flow tube from moving to the closed position. The spring-loaded releasable latch provides the necessary force by utilizing belleville spring washers which, while having limited deflection characteristics, will provide the large force required to keep a large area orifice valve in the open position. Preferably, the releasable latch is adjustable to change the force setting which the releasable latch exerts on the flow tube.